The overall objective of this research is to study the structure, metabolism and function of animal cell surfaces. This interest has been stimulated by recent evidence relating cell surfaces with regulations of cellular growth. It is the specific purpose of the present research project to understand the mechanism of density dependent synthesis of glycolipids in normal cells and to determine what factors alter this process when cells are transformed by tumorigenic viruses. Initial studies will be done with polyoma transformed and untransformed hamster cells (NIL lcl) since this normal cell line has only one glycolipid (hematoside) that is density dependent and is therefore one of the simplest cell systems to study this phenomenon. We will attempt to distinguish between the effects due to growth rate and those due to culture density by comparing growing and non growing sparse cells with dense cells which are also either growing or not growing. The glycolipid changes will be localized within the cell. The amount of hematoside in the plasma membrane and in intracellular membranes of sparse and dense cultures will be measured. We will also determine the amount of hematoside that is exposed on the cell surface. These results will be correlated with in vivo enzyme activities such as the possible presence of surface sialyl transferases and with in vitro activities. We will determine the generality of our observations by comparing them with normal and RSV-transformed chick cells. In this system mutants temperature sensitive for tranformation are available and one is thus able to circumvent the possibility that differences between normal and transformed cells are due to clonal variation.